Petrographic and diagenetic investigation of the distal Triassic ‘Budleighensis’ fluvial system in the Solway and Carlisle Basins for potential CO 2 storage

Abstract

Failure to find hydrocarbon prospects in the Solway Basin region has resulted in a lack of research into the local Sherwood Sandstone Group petrography, reservoir quality and depositional history compared to the analogous southern reservoirs in the EISB which will be utilized for carbon storage. A detailed petrographic study is presented which aims to understand if the Solway Firth could have similar utility. The Permo–Triassic Sherwood Sandstone Group is believed to be deposited in depocentres connected during the Early Triassic by the extensive ‘Budleighensis’ fluvial system. Here, the Solway and Carlisle basins are proposed as terminal sites for this endorheic system, with the Lower Triassic Annan Sandstone Formation ascribed to the distal region of a fluvial distributary zone and the overlying Kirklinton Sandstone Formation thought to mark a transition to a basinal zone, depositing aeolian sandstones and locally associated playa lake facies. Fluid inclusion, stable isotope burial history modelling and field observations have been used to assess the relative timing and importance of different diagenetic cements. Early diagenetic cements include grain-rimming haematite and patchy calcite cement, especially in the Annan Sandstone Formation. Later burial diagenesis sees further calcite cement, quartz overgrowths and, restricted to the Kirklinton Sandstone Formation, ferroan dolomite. Porosity and permeability show significant differences between fluvial Annan and aeolian Kirklinton facies associations. Despite the finer grain size, a reservoir with excellent porosity and permeability as well as no hydrocarbon charging or legacy hydrocarbon extraction is persevered, suggesting the Solway Basin could be a secure CO 2 storage site. This article is part of the Energy Geoscience Series available at https://www.lyellcollection.org/cc/energy-geoscience-series Supplementary material: An overview of the primary and secondary data collected and utilised in this study, as well as raw data values are available at https://doi.org/10.6084/m9.figshare.c.5906677